Topping the 90Prime dewar

We spent the evening last night training to use the 90Prime camera on the Steward Observatory 90 inch telescope for a night of observing this Thursday. One of the things that needs to be done is to top the CCD camera dewar with Liquid Nitrogen to keep the detector cold and reduce noise when observing faint objects. This image shows the 90 inch telescope with the prime focus camera dewar at right with what looks like a comet coming from the end of the dewar. That is just the nitrogen gas venting as the liquid is forced into the dewar. This image was taken with my 10mm fisheye lens with an exposure of 20 seconds at f/22, ISO 100. The long exposure not only allowed the motion of the venting to be smeared but also helps keep the entire image in focus with the small f-stop. It also gives a really cool star pattern to the lights in the background due to diffraction affects in the optics.